a. Field of the Invention
The present invention relates to reinforced laminates and to films for making such laminates. More particularly, the present invention relates to reinforced paper, textiles or the like incorporating at least one layer of an oriented slitted or apertured film.
B. Description of Prior Art.
Reinforced laminates using textiles, scrim or filaments of cotton, rayon, nylon, fiberglass, etc. placed between two layers of paper or the like are known and are widely used. It has also been proposed by applicant to replace the filaments, scrims or threads by narrow, highly oriented polymeric tapes. It has further been proposed to use fibrillated film such as fibrillated highly oriented polymeric film which is particularly suitable for materials having a high level of flexibility or drape, as in non-wovens.
Where the material is to be reinforced in two directions (i.e. in the machine direction and cross-machine direction) the disposition of cross-machine direction reinforcing threads, filaments or tapes, is generally performed by means of elaborate machinery involving alternating motion of a revolving turret onto which bobbins for the reinforcing materials are mounted. Such equipment is generally troublesome and requires heavy maintenance rendering continuous operation difficult.
When fibrillated film is used, it is generally preferred to spread the film to thereby reduce the total reinforcing material necessary. However, spreading of a fibrillated film is a difficult operation and causes twisting of the individual interconnected filaments or the like forming the fibrillated film and thereby limits the degree the fibrillated film may be open to depend on the width of the individual filaments so that a large open area film is limited to those films having relatively narrow individual filaments. Also the fibrillation pattern of the film sets limits on the degree to which it can be spread.
Fibrillated films from polyolefins have been used to make yarns, cordages and in other textile applications to replace natural fibers or conventionally spun yarns. The practice of fibrillation resulted from the observation that highly oriented film was easily fibrillatable and the method involves first orienting an orientable synthetic organic polymer film by stretching, preferably while heated, followed by fibrillation by one of numerous ways known in the trade. One way of post-orientation fibrillation is by running the film over a roll surfaced with a plurality of perforating pins. An endeavour of this procedure is to make fine denier fibers of high strength, relying on the orientation step to provide the strength and having the advantage of replacing the more complex spinning process.
Fibrillation of oriented polymeric films is well known in the art. Linear polymers, after being highly oriented monoaxially possess considerable strength in the orientation direction, but little strength in the transverse direction so that they can be fibrillated in various ways.
Some polymers, with low intermolecular forces, for example linear polyolefins can be fibrillated with ease. Others, due to their chemical composition or structure possess relatively strong intermolecular forces between adjacent polymer chains, making the fibrillation, by known means, difficult. Nylon is an example of such a polymer. Others are non-linear, or branched polymers, such as LDPE.
Another case where the present fibrillation methods fail is when film laminates, containing at least one layer of a difficult to fibrillate polymer are processed. For example, a low density polyethylene-polypropylene laminate offers resistance to the penetration of the fibrillating means, for example pins or hacksaw blades.
Still another instance where the present fibrillation methods fail is when a high degree of residual elongation is required in the fibrillated material. This is because a high degree of orientation is needed to obtain fibrillating properties and elongation to break decreases sharply with degree of orientation.
A further example of failure of the present fibrillation methods is when a very high degree of regularity is desired in the fibrillated film pattern, that is when the individual filament denier must be carefully controlled.
A major shortcoming of present fibrillation methods, is that the fibrillated film suffers a considerable drop in tensile elongation and thereby toughness or energy to rupture properties, as compared with the unfibrillated film. For example, a 1 inch wide strip about 1 ml. thick oriented polypropylene film will break under a load of 50 lbs. after an elongation of 10 to 15%. If the same film is fibrillated, then the resultant fibrillated film will break under a load of 10 to 30 lbs., after an elongation of 6 to 8% depending on the fibrillating means and the extent of fibrillation.